Hand held, foam guns are used to deliver beads, filets, globs, etc. of foam (e.g., polyurethane foams) that--upon curing--serve to seal cracks, holes and other openings through which undesired fluids would otherwise pass. For example, polyurethane foams are widely used in building construction to seal cracks against outside air and water leakage--as well as against insect invasion. Some foam guns dispense ready-made foams while others are designed to mix foam-making ingredients in the gun and then dispense the resulting foam product out of the gun's nozzle (see for example U.S. Pat. No. 4,550,863).
In many prior art foam application practices, foams (ready-made foams, provided in pressurized containers, as well as foams formulated in a foam gun just before it is dispensed) are dispensed through hose(s) carrying foam (or foam-making ingredients) from such containers to hand held applicator devices. These applicator devices often employed a ball valve, positioned near the applicator's outlet, to control the foam's flow at the applicator's dispensing nozzle. One of the chief drawbacks to this mode of foam application was the fact that there was a significant delay between the time the ball valve was turned off, and the time the foam actually stopped being dispensed from the applicator's nozzle. That is to say that, even after the ball valve completely stopped flow of the foam into the applicator, the foam beyond the shut off valve would auto-expand in the applicator and be forced out of its dispensing nozzle.
This continued foam flow is often referred to as "post-shutoff-drip." Post-shutoff-drip in such prior art devices often dispenses an additional 4 to 8 inch bead of foam after the shutoff valve is fully closed. At the very least, post-shutoff-drip wastes valuable foam; worse yet, the "excess" foam often overfills cracks and/or holes to such an extent that undesired humps or bulges of cured foam are created. These humps or bulges of cured foam often cause subsequent construction problems and/or conflicts between tradesman. For example, such humps may cause drywall that is laid over such humps of cured foam to bulge outward and make the drywall installer's job more difficult and less workmanlike. This very undesired effect is addressed in two ways: by labor intensive (and hence expensive) hand removal of such humps or bulges of cured foam and/or increased care and skill on the part of the foam gun operator.
Such care and skill implies that the operator learn to "anticipate" where a moving hand held applicator device will completely cease dispensing foam and learn to close the dispensing valve before the foam bead reaches its anticipated end point. If the operator stops the foam flow too soon, the crack, gap or other opening may not be completely filled. This may result in undesired fluid or insect invasion via that opening. To prevent this, the operator must perform a second caulking operation to correct his mistake. Such corrections waste the operator's valuable time. Conversely, if the operator stops the foam flow too late, waste--and, perhaps, undesired humps of cured foam--will result. Long periods of trial and error type experience are needed before most operators acquire the "knack" for such anticipatory valve shut off operations.
In response to this post-shutoff-drip problem, a new generation of hand held applicator devices was developed in the 1980's. These devices had a pistol-like design and were provided with a needle valve rod that seated, and thus shut off foam flow, at, or very near to, the foam gun's dispensing nozzle. This design feature made the operator's release of the trigger (to stop the foam's flow) much more contemporaneous with the actual shut off of the foam's flow. This desirable feature is often referred to as "positive-shutoff". In effect, this positive-shutoff follows from the fact that the gun's foam shut off valve is made a integral part of its dispensing nozzle. In effect, this arrangement places the valve's choke point within less than about a quarter inch of the nozzle's front tip. This results in minimal post-shutoff-drip (e.g., it is generally less than about one half inch using foam guns of this type).
Unfortunately, achievement of this ability to minimize post-shutoff-drip, introduced a new set of problems and aggravations. Not the least of these is the fact that these positive-shutoff nozzle tips are worn down very quickly as they are dragged across hard, rough surfaces such as concrete floors and walls. Such wear not only destroys the outer surface of the nozzle, it soon reaches the needle valve rod itself; and damage to these rods--and hence the valving action controlled by them--all too soon, leads to costly repairs and a great deal of expensive "down time" for such foam guns, and "lost time" for their operators.
Another problem with these positive-shutoff foam guns follows from the fact that their needle valve-containing nozzle ends are positioned so close to the gun barrel conveying the foam that the barrel's diameter (as opposed to the nozzle's generally "thinner" diameter) defines the width of the cracks, holes, etc. into which the nozzle tip can be inserted. For example, it is hard, or impossible, to get a gun's nozzle three or four inches deep into a one quarter inch wide crack, hole, etc. if the diameter of the barrel of the gun immediately behind the nozzle has an outside diameter of one half inch. Some manufacturers tried to solve this "too large of a barrel diameter" problem by tapering the nozzle end of the barrel to a diameter just slightly larger than the nozzle's diameter. Unfortunately, this tapered barrel approach tends to slow down foam flow to such an extent that there is a substantial increase in application time using foam guns having tapered barrels. This increases labor costs. Furthermore, these positive-shutoff foam guns tend to produce foam beads whose surfaces (or "skins") are of a lesser quality than prior art hand held applicator devices.
In response to these nozzle "accessibility," time loss and bead quality problems, a wide variety of "accessory tips" were developed. Most of these were especially adapted to dispense foam into gaps that are more narrow than a foam gun's barrel near its foam dispensing end. Unfortunately, problems and aggravations also arose with use of such accessory tips. By way of example, many of these accessory tips were designed to merely slide over the barrel and nozzle in a, not particularly tight, compression fit. Consequently, such accessory tips often slip off the end of the nozzle or gun barrel on which they are mounted when normal foam application pressures are applied and/or when the accessory tip is dragged across rough surfaces. Other kinds of prior art accessory tips tend to stay in place on the end of such guns; but, continue to have problems with foam leakage at their connection points with the gun barrel. Moreover, truly effective use of many prior art accessory tips often becomes a "two-handed" operation: that is to say that one hand is needed to hold the gun at its pistol grip and operates the trigger--while the fingers of the other hand hold the accessory tip firmly in place on the end of the gun barrel and/or accurately guide the accessory tip into cracks, holes, etc. Generally speaking, such two-handed operations are more tiring than one-handed operations. Two-handed operations also tend to introduce greater safety hazards into many work situations since foam gun operators often have to work from stepladders. Moreover, many of these accessory tips have, to a large degree, re-introduced the post-shutoff-drip problem. This follows from the fact that these accessory tips often have relatively large volumes; hence, they too continue to dispense their foam contents after the gun's shutoff valve is completely closed.